fixing a mistake (cylinder)

[standardsteam]

I hope nobody minds too much that I'm asking the community more than I'm contributing, but hopefully in time I'll may be able to assist.

Being still a fairly inexperienced "engineer", when I started machining the cylinders for my engine I made a very rough job of machining the transfer ports. Now many years later as the loco reaches completion I need to finish them off except that the ports are wildly off and need to be rectified if the loco is to be in any way successful. Short of starting again (and I have already fitted the covers and pistons) the only thing I can think of short starting again or attempting to fill the existing ports with spelter, is to machine a bronze plate with the ports at the correct spacing and skim the top of the cylinder hoping the joint could be made steam tight. Does anyone have any ideas how to rectify this error?

[ilvaporista]

Using an additional plate as you suggests works. I've done in on a 2 1/2" loco. You can make the joint steam tight by tinning the both the casting and plate with soft solder and then heating the lot together. I first made the mistake of making the plate too thin (0.5mm) and it buckled under heating. I also put in some bronze screws to hold everything together for soldering. The valve face came out slightly convex but it soon lapped flat. No problems with leakages between ports.

[ilvaporista]

Don't put too much solder on the parts to avoid problems with it running and blocking the ports

[Jo]

Before you machine off 1/8": have you considered silver soldering in some bronze in the offending ports and then re machining? I found this very successful when I had a milling cutter slip at the end of a port.

You need less bronze and if it fails you still have the option of machining off the 1/8" but will not have to pay for or wait for donor castings to arrive. I take it you are considering using a set of valve chest cover castings as donors for the major surgery.

Jo

[standardsteam]

I'm a little unsure of the nomenclature, "silver soldering some bronze"? I've worked with brass and silver solder as spelter, but not bronze. Is a different flux and rod required for bronze (it's a gunmetal cylinder)?

-- edit, now I'm with you, make a fillet out of bronze and solder it in!

On reason I haven't considered the hard solder option is because the mess most of my soldering comes out, not necessarily that the spelter is all over the place but the item is black and I have a nice smooth bore on the cylinder already which I can't see being maintained if I heat the lump to the required temperature and dump it in the pickle. I have got some citric acid type pickle which I could use cold I suppose, I haven't actually dunked a gunmetal casting in either yet, but I assume it holds up a bit better than copper. The last steel item I dumped in the pickle came out copper coated as it went in the same stuff my boiler went into, I think I must have left it in there too long!

[Jo]

Your bronze cylinder will darken with the heat but come out clean from a dunk in the pickle. I cannot see citric doing any damage to your bore even if you left it in all week! But you should need much less time than that. I personally use Sulphuric and it takes about 10 mins to pickle, but do not get it on your clothes or hands.

I suggest you make up your bronze plugs so that they are a reasonable fit, sitting slightly proud, flux them up drop them in the ports and then cut a few short lengths of silver solder placing on either side of the ports with their plugs in situ. Then using a propane torch heat up the cylinder, as soon as it is hot enough the silver solder will flash into the gap between the plug and cylinder, if necessary you can touch up with more silver solder if you have to: Job done. Let it cool and then let it have a swim in the pickle, take the plugs level with the surface and then re-machining the ports.

I would not let soft solder near my cylinders, in theory (but highly unlikley) super heated steam could melt it. I can imagine that soft solder would make a nasty mess in the heat of the torch.

Jo

[baggo]

The accurate cutting of slide valve ports seems to be a major stumbling block for a lot of builders. I've got half a dozen 2-1/2" gauge loco chassis's that I've picked up over the last year or so and only one has decent ports in the cylinders. The rest look as though they've been knawed out by a rat or something!

Although not directly related to this post, the following may be of interest as I've never seen the idea written down anywhere.

When I was machining the ports in my 2-1/2" gauge 3 cylinder Flying Scotsman I had visions of making the same mistakes myself so I made a port cutting jig. I cut a piece of mild steel the same size as the port face and marked the ports out on to it as well as the bolt holes for the steamchest. I then carefully drilled and filed the ports to size and then case hardened the plate. The jig was then used to mark out the steam chest fixing holes and the corner ones were drilled and tapped so that the jig could be bolted onto the port face. The ports were then drilled out and finish milled using the jig as a guide for the endmill. The hardened jig prevented any 'dig ins' and left perfectly finished ports. The photo below shows the jig in use on the middle cylinder.



An added bonus was that I only had to mark out the ports once instead of three times ;D

[Tel]

As long as the port face and the port plate are nice and flat the merest smear of RTV gasket compound will seal things nicelyt

[Jo]

John,

Sorry to be a bore: Wet steam at 100 psi is 164 deg F, but I am talking super heated steam which my steam tables identifies could go as high as 700 deg F.

Tubal Cain did the calculations in his Model Engineers handbook, in which he identified that had typical 5" loco super heater tubes can regularly deliver 500 degs ..

Jo

[greasemonkey]

Hi All
Dont user soft solder near your cylinders. I assembled the lubricator pipe work on my first simplex with soft solder. One winter run I managed to unsolder the joint at the base of the steam inlet whilst working the engine hard, and this joint hangs in the breaze!! All pipe work is now silver soldered!!

Andy

[John Lee]

jo said:

John,

Sorry to be a bore: Wet steam at 100 psi is 164 deg F, but I am talking super heated steam which my steam tables identifies could go as high as 700 deg F.

Tubal Cain did the calculations in his Model Engineers handbook, in which he identified that had typical 5" loco super heater tubes can regularly deliver 500 degs ..

Jo

If you were achieving 700 F, the silver soldered joints in your superheater would be your first problem.. getting close!

It will drop again as it goes through the smokebox and your piping.

Soft Solder is useful for assembling brass superstructure, maybe, just maybe, for caulking a leak well away from the fire and heat, but anything else needs silver solder IMHO

John

[spurley]

Has someone removed a post from this thread It doesn't seem to make sense anymore. I'm sure someone was doubting steam temperatures at one time.

Heh ho, never mind

Cheers

Brian

[waggy]

Where did the degrees F come into play? My guidelines for the melting points of solders are all in Centigrade (Celsius), not Fahrenheit (F).

Waggy.